The act of tampering refers to reading secret information from a memory device or altering secret information by unauthorized means, and in a broader sense, also includes the act of breaking into the case that houses a memory device. One such act of breaking into a case is, for example, the act of penetrating the board within a case with a thin needle-shaped tool. One known method of protecting a memory device, that is an object that is to be protected from tampering, employs a substrate surrounded by a conducting part for detection of tampering.
Compared to the boards that enclose the top and bottom of a memory device, the protective countermeasures applied in the sidewalls provided between these boards have been found, some cases, to be inadequate. As a strengthened protective measure for sidewalls, a method is disclosed in Patent Document 1 that consists of using protective boards, to which wires have been provided to detect tampering, to protect all surfaces.
In the device disclosed in Patent Document 1, wires are provided not only on the overlying and underlying protective boards but also on the protective boards of the side surfaces. In the device disclosed in this document, a single wire is arranged at a fixed spacing in a predetermined direction on the surface of each protective board, and this wire is connected to a tamper-monitoring circuit by way of a connector. By means of this configuration, when a person attempting to tamper pierces the protective board of a sidewall with a sharp tool, the wire is broken by the sharp tool, whereupon the tamper-monitoring circuit detects the act of tampering.